{DO you know how to make that  type real was 1234.12312 but not
1.23e+1&   How to make a round to third element after"."}
 program acm;

var a,b,r,s,sn,cs:real;x,y:integer;
st,st1,st2:string;
begin
readln(a,r);
if (a<=100) and (r<=100) then begin
if r<=(a/2) then begin s:=(pi)*r*r;    end;
if r>=(a/(sqrt(2))) then begin  s:=a*a;  end;
if  (r>(a/2)) and (r<(a/(sqrt(2)))) then  begin
sn:=sqrt(1-(a*a)/(4*r*r));
cs:=sqrt(1-sn*sn);
b:=arctan(sn/cs);
s:=(pi)*r*r-2*2*b*r*r+2*a*r*sn;
end;
x:=trunc(s);
if trunc(frac(s)*10)=0 then begin
y:=trunc(frac(s)*1000);

str(x,st);
str(y,st1);
 st2:=(st+'.'+'0'+st1);   end;

if trunc(frac(s)*100)=0 then begin
y:=trunc(frac(s)*1000);

str(x,st);
str(y,st1);
 st2:=(st+'.'+'00'+st1);   end;

if trunc(frac(s)*1000)=0 then begin
y:=trunc(frac(s));

str(x,st);
str(y,st1);
st2:=(st+'.'+'000');   end;

if trunc(frac(s)*10)<>0 then begin
y:=trunc(frac(s)*1000);

str(x,st);
str(y,st1);
 st2:=(st+'.'+st1);   end;


writeln(st2);
           end;
readln;
end.

writeln(R:0:3)